Warning: mysql_connect() [function.mysql-connect]: mysqlnd cannot connect toMySQL 4.1+ using old authentication in index.php on line 29

The script giving the error was running on OS X 10.6.4 with the stock PHP 5.3.1. After doing a bit of searching and reading the MySQL documentation on the old password format, I was a bit confused because I ran this on the server:

Both the server and client should support the new authentication version, which was introduced all the way back in MySQL 4.1. So why wouldn't it connect?

It turns out that CentOS 5 disables the new password hashes by default in favour of remaining compatible with 3.x (and earlier) MySQL clients. All you have to do is edit /etc/my.cnf and comment the old_passwords=1 line. After restarting the server, you should notice that running SELECT PASSWORD('foobar'); in a MySQL prompt will return 41-character hashes, not the old-style 16 character hashes. Reset the user passwords to start using the new hashes and you'll be good to go.

Although some users have reported success, most installations I've tried of MySQL 5.1 on Vista have failed, even on fresh Vista installs. The first problem appears at the end of the service instance configuration. All appears to be well, however the server refuses to start with Could not start MySQL service or Could not start the service MySQL. Error: 0.

The trick is to start MySQL from the console so that you are able to see the error message (you can access the command console by typing cmd into the Run dialog):

This message is a symptom of the log file size problem (just google InnoDB: Error: log file .\ib_logfile0 is of different size for more information). All you need to do is to clear the following files from the folder C:\ProgramData\MySQL\MySQL Server 5.1\data:

ib_logfile0ib_logfile1ibdata1$YOUR_HOSTNAME$.err

Restart the MySQL server and all should be well. Note that the C:\ProgramData\ folder is hidden, so unless you have enabled hidden folders from the Folder Options dialog, you will need to copy/paste that folder path directly into the address bar in order to access the folder.